The present invention is directed to a printing unit with a screen-printing cylinder. The screen printing cylinder has a movable doctor blade device. Two directly cooperating screen-printing cylinders, each with at least one working doctor blade, may also be provided.
EP 07 23 864 B1 has disclosed a printing unit for a rotary printing press. A first screen-printing cylinder, together with a second cylinder, forms a printing nip, in which a print stock is printed.
This known printing unit is only suitable for one-sided printing.
DE 26 38 344 A1 discloses two cooperating screen-printing cylinders.
JP 63-071350 A discloses two opposing printing cylinders, each with a doctor blade. A separation between a doctor blade and a counter-pressure device is not provided.
The object of the present invention is to provide a printing unit with a screen-printing cylinder.
The object is attained according to the invention by the provision of at least one screen-printing cylinder with a movable doctor blade. Two directly cooperating screen-printing cylinders can also be used. Each has a working doctor blade and a counter-pressure device. The counter-pressure device of one of the screen-printing cylinders supports the working doctor blade of the other screen-printing cylinder.
The advantages that can be achieved with the present invention are comprised particularly in the fact that the printing press permits first forme printing and second forme printing in the screen-printing process with matching registers to be executed in a single printing procedure.
To this end, the present invention provides that the second cylinder is also a screen-printing cylinder so that each screen-printing cylinder is used to print a respective side of a print stock being fed through the printing nip which is defined by the two screen-printing cylinders.
In order to permit an exact, register-matching printing, even at the edge of a sheet-like print stock, preferably at least one of the two screen-printing cylinders is equipped with a sheet gripping mechanism for the sheet-like print stock.
In order for this sheet gripping mechanism to be able to pass through the printing nip, it is necessary for at least one of the two screen-printing cylinders to have an indentation on its circumference surface. A doctor blade device disposed inside the screen-printing cylinder can preferably be moved radially so that it can move out of the way of the indentation.
It is also preferable for the doctor blade devices of the two screen-printing cylinders to each have a working doctor blade, each of which working doctor blades which touches the interior of the screen of its respective screen-printing cylinder when pressing ink through it, the respective working doctor blades of the two doctor blade devices being exactly aligned with each other, so that the working doctor blade of each doctor blade device compensates for a pressure exerted on its screen by the working doctor blade of the other. This arrangement provides the simple assurance that there is a sufficient pressure in the printing nip to press the ink required for the printing through the screens and to transfer it onto the print stock. On the other hand, an undesirable deformation of each screen by the pressure of the doctor blade device associated with it is prevented because the respective other doctor blade device exerts a corresponding counter-pressure.
Alternatively to this, each doctor blade device can also have a counter-pressure device spaced apart from its associated working doctor blade in the circumference direction of the screen-printing cylinder. Each such counter-pressure device is aligned with the respective working doctor blade of the other doctor blade device and compensates for the pressure which this other doctor blade device exerts.
In addition to their previously well-known and customary task of applying ink to the screen-printing cylinder, the doctor blade devices thus also perform the task of the counter-pressure cylinder that is usually provided.